Hi Al,

CC Michael/m68k,

On Mon, Jan 10, 2022 at 5:20 PM Al Viro [off-list ref] wrote:

On Mon, Jan 10, 2022 at 04:26:57PM +0100, Geert Uytterhoeven wrote:

quoted

On Mon, Jan 3, 2022 at 10:33 PM Eric W. Biederman [off-list ref] wrote:

quoted

The generic function ptrace_report_syscall does a little more
than syscall_trace on m68k.  The function ptrace_report_syscall
stops early if PT_TRACED is not set, it sets ptrace_message,
and returns the result of fatal_signal_pending.

Setting ptrace_message to a passed in value of 0 is effectively not
setting ptrace_message, making that additional work a noop.

Returning the result of fatal_signal_pending and letting the caller
ignore the result becomes a noop in this change.

When a process is ptraced, the flag PT_PTRACED is always set in
current->ptrace.  Testing for PT_PTRACED in ptrace_report_syscall is
just an optimization to fail early if the process is not ptraced.
Later on in ptrace_notify, ptrace_stop will test current->ptrace under
tasklist_lock and skip performing any work if the task is not ptraced.

Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: "Eric W. Biederman" <redacted>

As this depends on the removal of a parameter from
ptrace_report_syscall() earlier in this series:
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>

FWIW, I would suggest taking it a bit further: make syscall_trace_enter()
and syscall_trace_leave() in m68k ptrace.c unconditional, replace the
calls of syscall_trace() in entry.S with syscall_trace_enter() and
syscall_trace_leave() resp. and remove syscall_trace().

Geert, do you see any problems with that?  The only difference is that
current->ptrace_message would be set to 1 for ptrace stop on entry and
2 - on leave.  Currently m68k just has it 0 all along.

It is user-visible (the whole point is to let the tracer see which
stop it is - entry or exit one), so somebody using PTRACE_GETEVENTMSG
on syscall stops would start seeing 1 or 2 instead of "0 all along".
That's how it works on all other architectures (including m68k-nommu),
and I doubt that anything in userland will get broken.

Behaviour of PTRACE_GETEVENTMSG for other stops (fork, etc.) remains
as-is, of course.

In fact Michael did so in "[PATCH v7 1/2] m68k/kernel - wire up
syscall_trace_enter/leave for m68k"[1], but that's still stuck...

[1] https://lore.kernel.org/r/1624924520-17567-2-git-send-email-schmitzmic@gmail.com/ (local)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds